JPS60191473A - Time axis correcting device - Google Patents

Abstract

PURPOSE:To prevent deterioration of a playback video signal in phase by generating a sample pulse only when a playback color burst signal is present. CONSTITUTION:The output of a VCO5 is applied to a pi/2 phase shifter 11, whose phase output is inputted to a synchronous detector 12. A burst-gated playback signal is applied to the other input and its detection output is inputted to an AND gate 15 through a waveform shaper 14. The output of a generator 9 is applied to the other input of this gate 15 and an S/H circuit 7 performs sample holding operation with the output of the gate 15. The synchronous detector 12 detects whether the playback burst signal is present or not and generates and supplies a gate signal for the gate 15 to the S/H circuit 7 only during the presence period. The gate 15 is closed in other periods, so the S/H circuit 7 holds the last error signal without performing sampling operation and the signal is used as the control signal of a variable phase shifter 10. Consequently, the generation of a time-axis error signal is prevented owing to the absence of the playback burst signal or malfunction of a PLL circuit.

Description

TECHNICAL FIELD The present invention relates to a time axis correction device, and more particularly to a device for correcting the time axis of a reproduced color video signal.

1" E: The signal reproduced from the video information recording medium is subjected to disturbances in the time axis direction, and therefore the reproduced image quality deteriorates. Therefore, time axis correction means are added. For example, in video disc players, a spindle servo is applied to the spindle motor that rotates the video disc to remove ultra-low frequency fluctuations in the time axis, and the center of rotation of the disc is 10-30 Hz due to eccentricity between the center of the recording track and the center of the recording track.
A so-called tangential servo is added to disturbances that cause component and higher frequency time axis fluctuations, and the reproduction R
Time axis fluctuations are removed at the F (high frequency) signal stage.

However, since these closed-loop servos may actually amplify disturbance components, the reproduced video signal is phase modulated to eliminate residual time base errors as shown in FIG.

That is, a sync separator 1 separates a sync signal from the reproduced video signal, and a gate pulse generator 2 generates a gate pulse synchronized with the horizontal sync signal. Of the chroma components separated and extracted from the reproduced video signal by a BPF (band pass filter) 3, only the color burst signal is gated by a gate pulse at a burst gate 4.

This gated burst signal and the output of the VCO (voltage controlled oscillator) 5 are compared by a phase comparator 6, and the comparison output is sampled by an S/H (sample and hold) circuit 7. This sample pulse is synchronized with the horizontal synchronizing signal and is generated by the sample pulse generator 9.

This sampling output is passed through loop filter 8 to VC
This is a control signal for O5, and constitutes a so-called PLI-control loop. The sampling signal serves as a control signal for the variable phase shifter 10 that controls the phase of the reproduced video signal.

By doing this, the time axis fluctuation component remaining in the reproduced video signal is removed.

In such a configuration, the control signal of the variable phase shifter 10 depends on the reproduction burst, so when the burst signal is missing or during the vertical synchronization signal period where there is no burst signal,
This control signal contains noise components,
Therefore, this causes the phase of the reproduced video signal to deteriorate.

11th column" An object of the present invention is to provide a time axis correction device that detects the presence or absence of a reproduced burst signal to prevent phase deterioration of a reproduced video signal.

The time axis correction device according to the present invention obtains phase error information of a reproduced color burst signal by sampling it using a sample pulse synchronized with a horizontal synchronization signal separated from a reproduced color video signal, and uses this phase error information to obtain the phase error information of the reproduced color burst signal. A time axis correction device for correcting a time axis, characterized in that it is provided with means for generating a sample pulse only when a reproduced color burst signal is present.

Example The present invention will be described in detail below using the drawings.

FIG. 2 shows one embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals. To explain the difference from FIG. 1, the output of the VCO 5 is applied to the π/2 phase shifter 11, and this phase output is used as the output of the synchronous detector 12. A burst-gated reproduced burst signal is applied to the other inputs, and the detected output passes through the LPF 13 and the waveform shaper 14 and becomes the output of the AND gate 15.

The output of the sample pulse generator 9 is applied to the external power of the gate 15. The output of the gate 15 causes the S/H circuit 7 to perform a sample and hold operation.

By doing this, the presence or absence of the reproduced burst signal is detected by the synchronous detector 12, and the gate 15 is activated only during the existence period of the reproduced burst signal.
A gate signal is generated for the sample pulse S
/H circuit 7. Since the gate 15 is closed during the other periods, the S/H circuit 7 does not perform any sampling operation, and the immediately preceding error signal is held and becomes the control signal for the variable phase shifter 10.

FIG. 3 is a signal waveform diagram of each part of the device shown in FIG. 2, and (A)
-(H) are the corresponding waveforms of the respective parts signals (A)-(H) in FIG. Here, the VCO 5 is driven by the average phase variation of the reproduced burst signal, and if a balanced phase detector is used as the phase shift comparator 6, the phase difference between these two forces will be π/2. Therefore, the phase shifter 11
The output of O5 is phase-shifted by π/2, and the reproduced burst signal is synchronously detected by the synchronous detector 12. Therefore,
The detection output becomes as shown in (E), and the presence or absence of a reproduction burst is determined. This signal (E) passes through LPF13 (F)
The waveform shaper 14 shapes the gate pulse as shown in (G). Therefore, if there is no regeneration burst, no gate pulse will occur, so
The S/H circuit 7 remains in a hold state and holds the immediately preceding error signal as a control signal for the variable phase shifter 10.

FIG. 4 is a block diagram for explaining another embodiment of the present invention, and is an example of a color signal low frequency conversion type VTR. The reproduced low frequency color signal (688KH2) is mixer 1.
6, the signal is multiplied by the output of the VCO 19 having an oscillation frequency of 4.27 MHz, and converted into a color signal of 3.58 MHz, which is the difference component. This signal is phase-compared with the reference signal 6- in the phase comparator 17, and the error component is passed through the equalizer 18 and becomes a control signal for the VCO 19. The jitter of the reproduced signal is corrected by the above closed loop, and the residual jitter is further corrected by the closed loop of the variable phase shifter 10 and the PLL circuit 20 in the next stage, as in the case of the video disk player shown in FIG. . In this case, as in the example in Figure 2, the presence or absence of a reproduction burst signal is detected and the PL is activated only when it is present.
If the S/8 circuit in the L circuit 20 performs a sampling operation, accurate time axis correction becomes possible.

Effects As described above, according to the present invention, it is possible to prevent the PLL circuit from malfunctioning and generating an erroneous time axis error signal when the reproduced burst signal disappears due to dropout or the like or during a non-burst period. Therefore, accurate time axis control is always possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional time axis correction device, Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is an operation waveform diagram of each part of the device of Fig. 2, and Fig. 4 is a block diagram of a conventional time axis correction device. FIG. 2 is a block diagram illustrating an embodiment of the present invention. Explanation of symbols of main parts 4... Burst gate 5... vCO 6... Phase comparator 7... S/8 circuit 9...・Sample pulse generator 12... Synchronous detector 15... ANDGATE Applicant Pioneer Co., Ltd. Agent Patent attorney Motohiko Fujimura

Claims (1)

[Claims] Phase error information of the reproduced color burst signal is obtained by sampling the phase error information of the reproduced color burst signal using a sample pulse synchronized with a horizontal synchronization signal separated from the reproduced color video signal, and the time axis of the reproduced color video signal is corrected using this phase error information. What is claimed is: 1. A time axis correction device, comprising means for generating the sample pulse only when the reproduced color burst signal is present.